1. Field of the Invention
This invention relates generally to semi-conductor laser diode-waveguide combinations and more particularly to a construction for a laser diode or waveguide that facilitates accurate coupling of the laser diode with a waveguide device.
2. Description of the Related Art
Semiconductor laser diodes emit light from an area that is usually less than one micron in thickness and a few microns wide. The light beam emitted by a laser diode is normally highly divergent, typically 10 to 30 degrees. There is a need for way to couple light from such a semiconductor laser diode to a waveguide or similar device that is itself no more than a few microns thin and several microns wide in cross section. For convenience, we will use the term "waveguide" to refer not only to waveguides per se, but also to other optical or electro optical devices having similar physical characteristics, including, for example, frequency converters, modulators, beam deflectors and the like.
The efficiency of coupling between a laser diode and a waveguide is critically dependent upon the accuracy with which the laser diode and waveguide are aligned, especially their vertical alignment. Heretofore, laser diodes and waveguides have been formed as separately discrete structures and mechanically aligned, for example, by edge coupling, prison coupling, or grating coupling. Edge coupling can be particularly efficient and a number of related approaches have been used, including physically placing a laser diode against the waveguide, or coupling the light to an optical fiber and then edge coupling the fiber to the waveguide, or focusing the laser beam from the fiber on the edge of the waveguide. All of these methods require accurate alignment of the light source, be it the laser diode or the optical fiber, with the waveguide, in three directions. Because of the critical dependence of coupling efficiency on accuracy of alignment, alignment to better than 0.1 micron accuracy is desirable.